Ultrasound from a focused ultrasonic transducer can be used to selectively treat regions within the interior of the body. Ultrasonic waves are transmitted as high energy mechanical vibrations. These vibrations induce tissue heating as they are damped, and they can also lead to cavitation. Both tissue heating and cavitation can be used to destroy tissue in a clinical setting. However, heating tissue with ultrasound is easier to control than cavitation. Ultrasonic treatments can be used to ablate tissue and to kill regions of cancer cells selectively. This technique has been applied to the treatment of uterine fibroids, and has reduced the need for hysterectomy procedures.
To selectively treat tissue, a focused ultrasonic transducer can be used to focus the ultrasound on a particular treatment volume. The transducer is typically mounted within a medium, such as degassed water, that is able to transmit ultrasound. Actuators are then used to adjust the position of the ultrasonic transducer and thereby adjust the tissue region that is being treated. However, it is often not possible to focus ultrasound beams in the vicinity of bone and tissue boundaries and also in the vicinity of air and tissue boundaries. This prevents ultrasound treatment of many regions of the body. Examples are the ablation of tissue from the prostate with standard transducer arrays and the treatment of tumors in the lungs.
US patent application US2008/0045865 discloses exposing nanoparticles to electromagnetic radiation, excluding radio-frequency radiation, to induce bubbles. The patient is then exposed to ultrasound which induces cavitation of the bubbles and generates heat in the vicinity of the nanoparticles.